Coupling



FIG. 1 is a top, front, isometric view of the coupling;

FIG. 2 is a front, plan view thereof; the left, right and back, plan views being mirror images thereof; and,

FIG. 3 is a top, plan view thereof; the bottom, plan view being a mirror image thereof.

The broken lines depict portions of the coupling and form no part of the claimed design. 

CLAIM The ornamental design for a coupling, as shown and described. 